I. Field of the Invention
This invention relates generally to electromechanical switching apparatus and more specifically to the novel design of a double-pole, single-throw switch having a momentary make, momentary break feature. An alternative embodiment provides a similar arrangement, but having a momentary make and a continuous on, continuous off feature.
II. Description of the Prior Art
Many forms of double-pole, single-throw toggle type electrical switches are known in the art. A typical arrangement of such a switch is set out in the Schmidt U.S. Pat. No. 2,899,513. In this configuration three separate contacts are provided and when the toggle lever is in a first position, continuity is established between a first and a second contact, whereas when the toggle lever is in its opposite position, continuity is established between the first contact and a third contact. In certain applications, such as starting circuits for electric motors, it is desirable to have a double-pole, single-throw toggle switch in which a first set of contacts are only momentarily closed during the actuation from an OFF to a ON condition. During the momentary closure of the contacts, a current path may be established to the motor starting relay, allowing its contacts to close so as to connect the motor across the supply lines. Such an arrangement also includes a set of auxiliary relay contacts which serve to latch the relay coil across the lines to thereby maintain it in its energized condition. Thus, the motor continue to be energized so long as current continues to flow through the control relay. To turn off the motor, it is desirable that the electrical switch employed will momentarily break the electrical circuit energizing the relay. The momentary interruption of the current through the relay causes its contacts to open which disconnects the motor from the supply lines and also opens the auxiliary latching contact on the relay.
Prior art arrangements for use in motor control circuits have utilized separate START switches and STOP switches which are connected in series with the motor control relay across the supply mains. The START switch is generally of the normally open variety while the STOP switch is a normally closed arrangement. Thus, closure of the START switch completes a circuit through the control relay, the relay having a set of latching contacts which are effectively in parallel with the START switch contacts such that the START switch contacts may be re-opened without breaking the series circuit through the control relay. The operation of the STOP switch breaks the current path through the control relay, causing its contacts to drop out and disconnect the motor from the line.
The switch device of the present invention simplifies the motor Start-Stop control structure in that it provides in a unitary package of double-pole, single-throw switch which serves the same function as the prior art, separate START and STOP switches used in motor control applications.